Photosensitive recording material, photosensitive recording medium, and process for producing hologram using this photosensitive recording medium

ABSTRACT

A photosensitive recording material comprising a solvent-soluble, thermosetting epoxy oligomer capable of cationic polymerization, an aliphatic monomer having at least one ethylenically unsaturated bond, the monomer being liquid at normal temperature and pressure, having a boiling point of 100° C. or above at normal pressure and being capable of radical polymerization, a photoinitiator selected from the group consisting of i) a first photoinitiator capable of simultaneously generating a radical species that activates radical polymerization and a Br.o slashed.nsted acid or Lewis acid that activates cationic polymerization, upon exposure to actinic radiation, and ii) a second photoinitiator comprised of a radical polymerization photoinitiator capable of generating a radical species that activates radical polymerization upon exposure to actinic radiation and a cationic polymerization photoinitiator capable of generating a Br.o slashed.nsted acid or Lewis acid that activates cationic polymerization upon exposure to actinic radiation, and a spectral sensitizer that sensitizes the first photoinitiator or second photoinitiator; the aliphatic monomer being mixed in an amount of from 20 parts by weight to 80 parts by weight based on 100 parts by weight of the thermosetting epoxy oligomer. Use of this photosensitive recording material is effective for producing a volume type phase hologram having superior diffraction efficiency, transparency and weatherability such as thermal resistance and being chemically stable.

This application is a Continuation of application Ser. No. 08/404,765filed Mar. 15, 1995, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a photosensitive recording material and aphotosensitive recording medium that are used to form a volume typephase hologram, and a process for producing a hologram using such aphotosensitive recording medium. More particularly, it relates to aphotosensitive recording material and a photosensitive recording mediumthat have a high sensitivity to visible light, in particular, to argonlaser light and electron rays, also have superior weatherability andstorage stability and have good hologram characteristic values for,e.g., resolution, diffraction efficiency and transparency, and a processfor producing a hologram using such a photosensitive recording medium.

2. Description of the Prior Art

Holograms enable reproduction of three-dimensional stereoscopic images,and hence have been hitherto used in covers of books, magazines or thelike, pop art display, gifts and so forth on account of their attractivedesignability and decorative effect. Holograms can also be said to beequivalent to records of information in submicroscopic units, and hencethey are also used as marks for preventing forgery of marketablesecurities, credit cards and so forth.

In particular, in volume type phase holograms, spatial interferencefringes with differences in not optical absorption but in refractiveindexes are formed in photosensitive recording mediums, whereby phasescan be modulated without absorption of light beams passing throughimages. Hence, in recent years, they are not only used for display butalso expected to be applied in hologram optical elements (HOE) astypified by head-up display (HUD) on the windshield of cars.

Now, recording materials for forming the volume type phase holograms arerequired to be highly sensitive to laser light having visibleoscillation wavelength and besides to show a high resolution. Whenactually used in forming holograms, they are also required to provideholograms having characteristics such as diffraction efficiency,wavelength reproducibility of reproducing light, band width (half widthof a peak of reproducing light) and so forth suited for their purposes.In particular, recording mediums for HUD holograms should preferablyhave the properties that the diffraction efficiency is 90% or more atspatial frequency of 5,000 to 6,000 lines/m, the half width of a peak ofreproducing light (the band width) is 20 to 30 nm and the peakwavelength of reproducing wavelength is within 5 nm of photographingwavelength, and are also required to have a good storage stability overa long period of time.

The general principle concerning the production of holograms isdescribed in some publications and technical books, for example, JunpeiTsuJinai, "Holographic Display", Chapter 2, Sangyo Tosho Co. Accordingto these, one beam of a coherent optical system with dual light fluxes,which is commonly a laser, is directed to a recording object, and aphotosensitive recording medium as exemplified by a photographic dryplate is placed at a position where the total-reflected light can bereceived. In addition to the beam reflected from the object, anothercoherent beam is directed into the recording medium directly withoutstriking the object. The beam reflected from the object is called theobject beam, and the beam directed to the recording medium, thereference beam. Interference fringes composed of the reference beam andthe object beam are recorded as image information (a hologram). Next,the recording medium having been processed is irradiated by light andviewed at a suitable position, where the light from an illuminationsource is diffracted by the hologram so as to reproduce the wave frontof the reflected light having first reached the recording medium fromthe object at the time of recording. As a result, an object imagesimilar to an actual image of the object is three-dimensionally seen.Holograms formed by making the object beam and reference beam incidenton the recording medium from the same direction are known astransmission holograms. In contrast thereto, holograms formed by makingthem each other incident from the opposite side of the recording mediumare commonly known as reflection holograms. The transmission hologramscan be obtained by known methods as disclosed in, for example, U.S. Pat.Nos. 3,506,327 and No. 3,894,787. The reflection holograms can beobtained by known methods as disclosed in, for example, U.S. Pat. No.3,532,406.

As a value for comparing holographic characteristics of holograms formedas images, refractive index modulation is used. This is a valuecalculated from the measured diffraction efficiency and recording mediumthickness, the former being the proportion of incident light diffractedby a diffraction grating which is prepared while directly irradiating arecording medium in the manner that dual light fluxes are at the sameangles to the recording medium. The refractive index modulation is aquantitative measure of the changes in refractive index that occur atexposed areas and unexposed areas of a volume hologram, i.e., theportions where light rays interfere with one another to become strong orweak in intensity, and can be found by the Kogelnik's theoreticalformula (Bell. Syst. Tech. J., 48, 2909, 1969). In general, thereflection holograms have more interference fringes formed per 1 mm thanthe transmission holograms and hence make it difficult to carry outrecording, so that it is difficult to obtain a high refractive indexmodulation.

As recording materials for such volume type phase holograms,photosensitive materials of bleached silver salt and dichromated gelatintypes have been hitherto commonly used. The dichromated gelatin typephotosensitive materials are materials most widely used in the recordingof volume type phase holograms, because of their high diffractionefficiency and low noise characteristics. Such photosensitive materials,however, have so short a storage lifetime that they must be preparedevery time the holograms are produced. Also, since the development iscarried out by the wet process, holograms may undergo deformation in thecourse of swell and shrink of the gelatin required when holograms areproduced. Hence, such materials have the problem that holograms have apoor reproducibility. As for the silver salt photosensitive materials,they require complicated processing after recording, and they arephotosensitive materials that can not be satisfactory in view ofstability and workability. These aforesaid photosensitive materials alsoall have the problem that they have inferior environmental properties asexemplified by humidity resistance and weatherability.

To overcome such problems, as materials having superior environmentalproperties and other properties to be possessed by hologram recordingmaterials, such as a high resolution and a high diffraction efficiency,hologram recording materials making use of poly-N-vinylcarbazole areknown in the art. For example, a hologram recording material comprisinga cross-linking agent cyclic cis-α-dicarbonyl compound and a sensitizer(Japanese Patent Application Laid-open No. 60-45283), a hologramrecording material comprising a1,4,5,6,7,7-hexachloro-5-norbornene-2,3-dicarboxylic anhydride and a dye(Japanese Patent Application Laid-open No. 60-227280), a hologramrecording material comprising 2,3-bornanedione and Thioflavine (JapanesePatent Application Laid-open No. 60-260080), a hologram recordingmaterial comprising Thioflavine T and iodoform (Japanese PatentApplication Laid-open No. 62-123489) and so forth are proposed. Since,however, these hologram recording materials still also require thewet-process development, they require complicated processing steps andhave the problem of a poor reproducibility. Since also they arephotosensitive materials mainly composed of poly-N-vinylcarbazole,though being chemically stable and having a high resolution and superiorenvironmental properties, the poly-N-vinylcarbazole tends to turn whiteupon crystallization, and has the problems that they have a poorreproducibility of transparency and solvents are limited. In addition,they are desired to be more improved in view of sensitivitycharacteristics.

As recording materials capable of being photocured at a highsensitivity, a photocuring resin composition used in combination of a3-ketocoumarin dye with a diallyl iodonium salt which are constituentsof a photopolymerization initiator (Japanese Patent ApplicationLaid-open No. 60-88005) and also a hologram recording material comprisedof such a photopolymerization initiator and a support polymerpoly(methyl methacrylate) in combination (Japanese Patent ApplicationLaid-open No. 4-31590) are proposed. These recording materials arechemically stable and have a high resolution and a high sensitivity, butare accompanied by formation of holes or pores on account of wetprocessing. Hence, they have the problems that the peak wavelength ofreproducing wavelength becomes non-uniform, the half width of the peakwavelength expands and also, when developed, uneven development tends tooccur because of a more or less resolution of supporting polymers inswelling solvent, and still also the presence of a large number of holesor pores in the hologram results in poor thermal resistance andthermopressure resistance.

As a measure for overcoming such problems, photopolymerization typephotosensitive materials that enable production of a hologram through asole processing step without any wet processing are disclosed in U.S.Pat. Nos. 3,993,485 and 3,658,526. The former discloses two types ofphotosensitive materials. A first example is a photosensitive resincomposition comprised of combination of i) two polymerizableethylenically unsaturated monomers having different reactivities andrefractive indexes with ii) a photopolymerization initiator, asexemplified by a cyclohexyl methacrylate, N-vinylcarbazole and benzoinmethyl ether system, which is held between two glass sheets, followed byexposure using a dual light flux optical system to record a hologram. Asecond example is a photosensitive resin composition comprised of fourcomponents, i.e., a polymerizable ethylenically unsaturated monomer andan ethylenically unsaturated monomer acting as a cross-linking agentwhen the former is polymerized, both having substantially the samedegree of refractive index, a non-reactive compound having a differentrefractive index than the two monomers, and a polymerization initiator,as exemplified by a butyl methacrylate, ethylene glycol dimethacrylate,1-phenylnaphthalene and benzoin methyl ether system, which can produce ahologram in the same manner as the first example. Whicheverphotosensitive resin compositions are used, the polymerization ofmonomers having higher reactivity proceeds at areas where theinterference fringes formed by the dual light flux optical system have astrong light intensity and at the same time the density gradation occursin monomers to cause the monomers with a high reactivity to be diffusedin the areas with a strong light intensity and cause the monomers with alow reactivity or non-reactive compounds to be diffused in the areaswith a weak light intensity. Thus, the interference fringes are recordedaccording to differences in refractive indexes to form a volume typephase hologram.

However, such hologram recording photosensitive resin compositions havehad the following problems. In the composition shown in the firstexample, the monomers with a low reactivity undergo polymerization to acertain degree, and no high refractive index modulation can be obtained.In the second example, the non-reactive compound 1-phenylnaphthalene ispresent in the system as a compound with a low molecular weight evenafter the hologram has been finished, resulting in no storage stability.Also, in both the examples, since they are mixtures having a lowmolecular weight and have a low viscosity, they can be held betweensubstrates with difficulty or can form thick films with difficulty,having many problems on workability and reproducibility.

As for the latter U.S. Pat. No. 3,658,526, it discloses a process forproducing a stable hologram formed of a hologram recording materialcomprising a polymer matrix incorporated with a photopolymerizableethylenic monomer and a photopolymerization initiator, according towhich a permanent volume type phase hologram can be obtained by one-timeexposure to actinic radiation. The hologram thus formed is fixed bysubsequent overall irradiation with actinic radiation. The hologramrecording material disclosed in that publication aims at many advantagesin view of workability and reproducibility, but has a low diffractionefficiency. In this hologram recording material, the hologram finishedhas a refractive index modulation ranging from 0.001 to 0.003. As aresult, the reproduced images of the hologram formed can only have alimited brightness. The brightness may possibly be improved to a certainextent by increasing the thickness of the hologram recorded layer. Thismeasure to solve the problem, however, consequently forces manufacturersto use hologram recording materials in a large quantity, and also causesa difficulty when holograms are used as fixtures in laminated safetyglass as in HUD on the windshield of cars. It should be also noted thatthe holograms obtained by this process usually cause a decrease indiffraction efficiency after storage for a long time.

Now, improvement techniques including the production of hologramrecording materials disclosed in this U.S. Pat. No. 3,658,526 aredisclosed in U.S. Pat. Nos. 4,942,112 and 5,098,803. These publicationsdisclose a composition basically consisting of a thermoplastic resin, apolymerizable ethylenically unsaturated monomer and aphotopolymerization initiator, where a compound having an aromatic ringis used in either the thermoplastic resin or the polymerizableethylenically unsaturated monomer in order to improve refractive indexmodulation, so as to provide a difference in refractive index. Since,however, similar to what is disclosed in U.S. Pat. No. 3,658,526, aresin with a high molecular weight is used as a binder matrix, there isa limit on the diffusibility of monomers at the time of exposure, sothat a large amount of exposure becomes necessary and also no highdiffraction efficiency can be obtained. To eliminate this disadvantage,a non-reactive plasticizer is added. The use of such a plasticizer,however, causes a problem on the film strength of the hologram formed,and also such a non-reactive plasticizer is present in the system as acompound with a low molecular weight even after the hologram has beenfinished, resulting in no storage stability. In addition, since thecarrier that holds the monomers and so forth is a thermoplastic resin,there is a disadvantage that the hologram has a poor thermal resistance.

As a proposal to eliminate such a disadvantage, Japanese PatentApplication Laid-open No. 5-107999 discloses a recording material inwhich the plasticizer disclosed in the above patent is replaced with acationic polymerizable monomer and a cationic polymerization initiatorso that the problems caused by the non-reactive plasticizer remainingafter the formation of holograms can be solved.

This recording material, however, requires a reasonable irradiation withlight to fix the hologram after its formation, and also, at the time offixing, the hologram formed may cause a strain because of diffusion ofthe cationic polymerizable monomer with a low molecular weight to makeit impossible to obtain a high diffraction efficiency. Since also,similar to the prior art thereof, the carrier that holds the monomersand so forth is a thermoplastic resin, there is a disadvantage that thehologram has a poor thermal resistance. Moreover, in a system where noresin binder is used as the carrier for holding them, the recordingmaterial can be held between substrates with difficulty because of a lowviscosity or can form thick films with difficulty, having many problemson workability and reproducibility.

Under such technical backgrounds, Japanese Patent Application Laid-openNo. 5-94014 discloses, as an improvement of the recording materialsdisclosed in the above U.S. Pat. Nos. 4,942,112 and 5,098,803 andJapanese Patent Application Laid-open No. 5-107999, a hologramphotosensitive resin composition comprised of an epoxy resin, a radicalpolymerizable ethylenically unsaturated monomer and a radicalphotopolymerization initiator.

So far as seen in Examples disclosed in the above Japanese PatentApplication Laid-open No. 5-94014, the hologram photosensitive resincomposition makes use of two kinds of epoxy resins. When, however,ultraviolet-curing epoxy resin is used, troublesome operations arerequired such that the radical polymerization and the cationicpolymerization are carried out under light with different wavelengthregions, and also, in order to control the diffusibility of monomers, amicroadjustment control is required such that the viscosity is increasedby preexposure. Thus, this composition still has the problem ofdifficulties in workability and reproducibility. When thermosettingepoxy resin and a curing agent are used, it takes a reasonableultraviolet-curing and heating time to cure the epoxy resin for thefixing, resulting in a very poor workability. In addition, theimprovement technique disclosed in this publication has a great problemthat no high diffraction efficiency can be obtained.

As discussed above, the photopolymerization type photosensitivematerials that enable production of a hologram by the sole processingstep without any wet processing have the problem on polymerizability anddiffusibility of monomers for obtaining a high refractive indexmodulation and the problem on storage stability caused by the additionof the monomer-holding carrier and the non-reactive additive. Inaddition, they can not obtain photosensitive recording materials andphotosensitive recording mediums having a good workability for producingholograms and good holographic performances such as hologram diffractionefficiency, transparency and reproducibility. Thus, it is still soughtto provide a photopolymerizable composition improved for the hologramrecording. In particular, it can be said to be natural to do so withregard to HOEs produced using the same.

SUMMARY OF THE INVENTION

The present invention was made taking account of the problems asdiscussed above. Accordingly, an object of the present invention is toprovide a photosensitive recording material and a photosensitiverecording medium that are used to form a hologram having superiorchemical stability, e.g., environmental resistance, in particular,thermal resistance, produced by dry processing, and having a highresolution, a high diffraction efficiency, a high transparency and asuperior reproducing wavelength reproducibility, and to provide aprocess for producing a hologram using such a photosensitive recordingmedium.

The photosensitive recording material according to the present inventioncomprises as main components;

a solvent-soluble, thermosetting epoxy oligomer capable of cationicpolymerization;

an aliphatic monomer having at least one ethylenically unsaturated bond,the monomer being liquid at normal temperature and pressure, having aboiling point of 100° C. or above at normal pressure and being capableof radical polymerization;

a photoinitiator selected from the group consisting of i) a firstphotoinitiator capable of simultaneously generating a radical speciesthat activates radical polymerization and a Br.o slashed.nsted acid orLewis acid that activates cationic polymerization, upon exposure toactinic radiation, and ii) a second photoinitiator comprised of aradical polymerization photoinitiator capable of generating a radicalspecies that activates radical polymerization upon exposure to actinicradiation and a cationic polymerization photoinitiator capable ofgenerating a Br.o slashed.nsted acid or Lewis acid that activatescationic polymerization upon exposure to actinic radiation; and

a spectral sensitizer that sensitizes the first photoinitiator or secondphotoinitiator;

the aliphatic monomer being mixed in an amount of from 20 parts byweight to 80 parts by weight based on 100 parts by weight of thethermosetting epoxy oligomer.

The photosensitive recording medium of the present invention comprises;

a substrate;

a photosensitive layer formed by coating on the substrate aphotosensitive solution comprising the above photosensitive recordingmaterial, followed by drying; and

an oxygen barrier layer provided on the photosensitive layer.

The process for producing a hologram using this photosensitive recordingmedium comprises the steps of;

subjecting the photosensitive layer of the above photosensitiverecording medium to holographic exposure to form a latent image,substantially directly followed by heating at a temperature of from 60°C. to 120° C. for 1 minute to 30 minutes to produce a volume type phasehologram.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D are views to illustrate the reaction mechanism of thephotosensitive recording material according to the present invention.

FIG. 2 cross-sectionally illustrates the constitution of thephotosensitive recording medium according to the present invention.

FIG. 3 schematically illustrates a dual light flux optical system usedin the photographing for holograms.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described below in detail.

The photosensitive recording material according to the present inventioncomprises as main components;

a solvent-soluble, thermosetting epoxy oligomer capable of cationicpolymerization;

an aliphatic monomer having at least one ethylenically unsaturated bond,the monomer being liquid at normal temperature and pressure, having aboiling point of 100° C. or above at normal pressure and being capableof radical polymerization;

a photoinitiator selected from the group consisting of i) a firstphotoinitiator capable of simultaneously generating a radical speciesthat activates radical polymerization and a Br.o slashed.nsted acid orLewis acid that activates cationic polymerization, upon exposure toactinic radiation, and ii) a second photoinitiator comprised of aradical polymerization photoinitiator capable of generating a radicalspecies that activates radical polymerization upon exposure to actinicradiation and a cationic polymerization photoinitiator capable ofgenerating a Br.o slashed.nsted acid or Lewis acid that activatescationic polymerization upon exposure to actinic radiation; and

a spectral sensitizer that sensitizes the first photoinitiator or secondphotoinitiator;

the aliphatic monomer being mixed in an amount of from 20 parts byweight to 80 parts by weight based on 100 parts by weight of thethermosetting epoxy oligomer.

As the above thermosetting epoxy oligomer, it is possible to use;

a thermosetting epoxy oligomer represented by Formula I: ##STR1##wherein R₁ and R₂ each represent a hydrogen atom, or a functional groupselected from a methyl group, an ethyl group or a trifluoromethyl group;and n is 1 to 20;

a thermosetting epoxy oligomer represented by Formula II: ##STR2##wherein n is 1 to 20; a thermosetting epoxy oligomer represented byFormula III: ##STR3## wherein R₃ represents a hydrogen atom or a methylgroup; X represents a hydrogen atom or a halogen atom; and n is 1 to 20;or

a thermosetting epoxy oligomer represented by Formula IV: ##STR4##wherein R₄ represents an alkyl group; and n is 1 to 20.

It is also possible to use a thermosetting bisphenol-A type epoxyoligomer represented by Formula V: ##STR5## wherein n is 1 to 20; andhaving an epoxy equivalent weight of from 400 to 6,000 and a meltingpoint of 60° C. or above.

It is still also possible to use a thermosetting epoxy oligomer suchthat a hydrogen atom bonded to a phenyl group in the thermosetting epoxyoligomer represented by Formula I or II has been substituted with ahalogen atom such as bromine or chlorine, or a thermosetting epoxyoligomer such that a hydrogen atom bonded to a phenyl group in thethermosetting epoxy oligomer represented by Formula V has beensubstituted with a halogen atom such as bromine or chlorine.

As the aliphatic monomer, it is preferable to use a polyethylene glycoldiacrylate or -methacrylate or polypropylene glycol diacrylate or-methacrylate represented by Formula VI: ##STR6## wherein R₅ to R₇ eachrepresent a hydrogen atom or a methyl group; and m and n are each 0 ormore and m+n is 1 to 20.

The first photoinitiator simultaneously generates a radical species thatactivates radical polymerization and a Br.o slashed.nsted acid or Lewisacid that activates cationic polymerization, upon exposure to actinicradiation. Compounds which can be used as the first photoinitiator mayinclude those selected from iron arene complexes,trihalogenomethyl-substituted s-triazines, sulfonium salts, diazoniumsalts, diaryliodonium salts, phosphonium salts, selenonium salts andarsonium salts. Specific examples thereof will be shown later.

The second photoinitiator is specifically a photoinitiator mixturecomprised of a radical polymerization photoinitiator capable ofgenerating a radical species that activates radical polymerization uponexposure to actinic radiation and a cationic polymerizationphotoinitiator capable of generating a Br.o slashed.nsted acid or Lewisacid that activates cationic polymerization upon exposure to actinicradiation. Specific examples thereof will be shown later.

The spectral sensitizer that sensitizes the first photoinitiator orsecond photoinitiator may include organic compounds selected fromcyanine or merocyanine derivatives, coumarin derivatives, chalconederivatives, xanthene derivatives, thioxanthene derivatives, azuleniumderivatives, squarilium derivatives, tetraphenylporphyrin derivatives,tetrabenzoporphyrin derivatives and tetrapyrazino derivatives. Specificexamples thereof will be shown later.

The photosensitive recording medium of the present invention which isobtained using the photosensitive recording material described abovecomprises;

a substrate;

a photosensitive layer formed by coating on the substrate aphotosensitive solution comprising a photosensitive recording material,followed by drying; the photosensitive recording material comprising asmain components a solvent-soluble, thermosetting epoxy oligomer capableof cationic polymerization, an aliphatic monomer having at least oneethylenically unsaturated bond, the monomer being liquid at normaltemperature and pressure, having a boiling point of 100° C. or above atnormal pressure and being capable of radical polymerization, aphotoinitiator selected from the group consisting of i) a firstphotoinitiator capable of simultaneously generating a radical speciesthat activates radical polymerization and a Br.o slashed.nsted acid orLewis acid that activates cationic polymerization, upon exposure toactinic radiation, and ii) a second photoinitiator comprised of aradical polymerization photoinitiator capable of generating a radicalspecies that activates radical polymerization upon exposure to actinicradiation and a cationic polymerization photoinitiator capable ofgenerating a Br.o slashed.nsted acid or Lewis acid that activatescationic polymerization upon exposure to actinic radiation, and aspectral sensitizer that sensitizes the first photoinitiator or secondphotoinitiator; the aliphatic monomer being mixed in an amount of from20 parts by weight to 80 parts by weight based on 100 parts by weight ofthe thermosetting epoxy oligomer; and

an oxygen barrier layer provided on the photosensitive layer.

The process for producing a hologram according to the present invention,which produces a volume type phase hologram using this photosensitiverecording medium, comprises the steps of;

subjecting a photosensitive layer of a photosensitive recording mediumto holographic exposure to form a latent image, substantially directlyfollowed by heating at a temperature of from 60° C. to 120° C. for 1minute to 30 minutes to produce a volume type phase hologram; thephotosensitive recording medium comprising;

a substrate;

a photosensitive layer formed by coating on the substrate aphotosensitive solution comprising a photosensitive recording material,followed by drying; the photosensitive recording material comprising asmain components a solvent-soluble, thermosetting epoxy oligomer capableof cationic polymerization, an aliphatic monomer having at least oneethylenically unsaturated bond, the monomer being liquid at normaltemperature and pressure, having a boiling point of 100° C. or above atnormal pressure and being capable of radical polymerization, aphotoinitiator selected from the group consisting of i) a firstphotoinitiator capable of simultaneously generating a radical speciesthat activates radical polymerization and a Br.o slashed.nsted acid orLewis acid that activates cationic polymerization, upon exposure toactinic radiation, and ii) a second photoinitiator comprised of aradical polymerization photoinitiator capable of generating a radicalspecies that activates radical polymerization upon exposure to actinicradiation and a cationic polymerization photoinitiator capable ofgenerating a Br.o slashed.nsted acid or Lewis acid that activatescationic polymerization upon exposure to actinic radiation, and aspectral sensitizer that sensitizes the first photoinitiator or secondphotoinitiator; the aliphatic monomer being mixed in an amount of from20 parts by weight to 80 parts by weight based on 100 parts by weight ofthe thermosetting epoxy oligomer; and

an oxygen barrier layer provided on the photosensitive layer.

Thus, the process for producing a hologram according to the presentinvention, which can produce a bright hologram on account of a highrefractive index modulation, can be achieved by carrying out suitableholographic exposure to form a latent image, substantially directlyfollowed by heating at a temperature of from 60° C. to 120° C. for 1minute to 30 minutes.

Incidentally, the improvement in diffraction efficiency that isattributable to the heat curing of thermosetting epoxy oligomers can notbe expected when overall exposure to ultraviolet rays or other actinicradiations such as electron rays, X-rays, visible light rays or infraredrays is carried out after the holographic exposure and before the heattreatment. Also, since in the present invention the high refractiveindex modulation is attained by the heat treatment, even the refractiveindex modulation of the level as disclosed in U.S. Pat. No. 3,658,526can be enough at the time of the holographic exposure, and such a highrefractive index modulation as disclosed in U.S. Pat. Nos. 4,942,112 and5,098,803 is not always necessary.

In the production processes according to the prior art in the abovepublications, it is explicitly stated that the recording medium isexposed to actinic radiation as a processing step and also that therefractive index of the hologram is controlled in a heating stepsubsequent to overall exposure. Hence, the photosensitive recordingmaterial and hologram production process according to the presentinvention in which the improvement in diffraction efficiency that isattributable to the heat curing of thermosetting epoxy oligomers can notbe expected when overall exposure to ultraviolet rays or other actinicradiations is carried out after the holographic exposure and before theheat treatment, are clearly distinguished from the above prior art.

In the compositional proportion and production process disclosed inJapanese Patent Application Laid-open No. 5-94104, no bright hologramcan be obtained at all, compared with the case when the photosensitiverecording material according to the present invention is used. Hence,the present invention is also distinguished from the prior art disclosedin Japanese Patent Application Laid-open No. 5-94104.

Now, as shown in FIG. 1A, in a photosensitive layer 3 formed of thephotosensitive recording material according to the present invention,aliphatic monomers 32 having at least one ethylenically unsaturatedbond, being capable of radical polymerization, and solvent-soluble,thermosetting epoxy oligomers 31 capable of cationic polymerization areuniformly distributed. In the hologram recording, upon exposure of thisphotosensitive layer 3 to laser interference light (i.e., light of thedual light flux optical system), the first photoinitiator or secondphotoinitiator in the photosensitive recording material simultaneouslygenerates radical species 34 that activate radical polymerization andBr.o slashed.nsted acid or Lewis acid 33 that activates cationicpolymerization, at portions undergoing a strong light interferenceaction among laser irradiated portions (FIG. 1B). The radical species 34generated here cause the aliphatic monomers 32 to undergo radicalpolymerization. As the monomers become polymerized, the photosensitiverecording material causes differences in density in its interior, sothat aliphatic monomers 32 move from the neighborhood to that portions.That is, as shown in FIG. 1B, the density of aliphatic monomers 32becomes higher at the portions undergoing a strong light interferenceaction among laser irradiated portions and the density thereof becomeslower at the portions undergoing a weak light interference action amonglaser irradiated portions. Thus, differences in refractive index areproduced between both the portions to effect hologram recording, as sopresumed.

After the exposure to laser interference light, a heat treatment isfurther applied, whereupon the Br.o slashed.nsted acid or Lewis acid 33simultaneously generated at the portions undergoing a strong lightinterference action during the laser interference light irradiation actsto cause the solvent-soluble, thermosetting epoxy oligomers 31 capableof cationic polymerization to undergo the cationic polymerizationaccording to light intensity distribution, so that presumably astructure with different crosslink density is formed (see FIGS. 1C and1D) and hence this contributes a more increase in the differences inrefractive index between the portions undergoing a strong lightinterference action and the portions undergoing a weak lightinterference action among the laser irradiated portions, thus making itpossible to obtain a volume type phase hologram having a highdiffraction efficiency, different from the prior art previouslydiscussed.

The reason why as previously stated the improvement in diffractionefficiency that is attributable to the heat curing of thermosettingepoxy oligomers can not be expected when overall exposure to ultravioletrays or other actinic radiations is carried out after the exposure tolaser interference light and before the heat treatment is presumed thatthe Br.o slashed.nsted acid or Lewis acid is uniformly generated as aresult of the overall exposure and consequently the crosslink densitybecomes uniform.

The thermosetting epoxy oligomer also serving as an image holding matrixturns to have a cross-linked structure attributable to the cationicpolymerization, so that the weatherability of the resulting volume typephase hologram can be improved.

Since also the first photoinitiator or cationic polymerizationphotoinitiator highly effective for generating the Br.o slashed.nstedacid or Lewis acid is used in combination with the spectral sensitizer,the Br.o slashed.nsted acid or Lewis acid that acts when thethermosetting epoxy oligomer serving as an image holding matrix is madeto have a cross-linked structure can be generated in a higherefficiency, so that the diffraction efficiency of the volume type phasehologram after heating can be more improved.

The photosensitive recording material according to the present inventionhas also a better reproducibility on the peak wavelength of reproducinglight and the band width thereof than conventional photosensitiverecording materials, and still also has a superior environmentalproperties. Hence, it can be applied to hologram optical devices.

The present invention will be further described below in greater detail.

FIG. 2 cross-sectionally illustrates the constitution of thephotosensitive recording medium according to the present invention. FIG.3 schematically illustrates a dual light flux optical system used in thephotographing for holograms.

The thermosetting epoxy oligomer which is one of constituents of thephotosensitive recording material according to the present invention mayinclude the solvent-soluble, thermosetting epoxy oligomer capable ofcationic polymerization, represented by Formulas I to IV as previouslydescribed. As examples thereof, they include epoxy compounds as shownbelow, produced by condensation reaction of a phenol compound of varioustypes such as bisphenol-A, bisphenol-AD, bisphenol-B, bisphenol-AF,bisphenol-S, novolak, o-cresol novolak and p-alkylphenol novolak withepichlorohydrin. Examples are by no means limited to these. ##STR7## (Inthe formulas, polymerization degree n is 1 to 20.) ##STR8## (In theformulas, R represents an alkyl group, and polymerization degree n is 1to 20.)

It is also possible to use a thermosetting bisphenol-A type epoxyoligomer represented by Formula V: ##STR9## wherein polymerizationdegree n is 1 to 20; and having an epoxy equivalent weight of from 400to 6,000 and a melting point of 60° C. or above. As examples thereof, itincludes usual commercially available products as typified by EPIKOTE1001, 1002, 1004, 1007, 1009, 1010 and 1100L, trade names, availablefrom Yuka Shell Epoxy K.K.; ARALDITE 6071, 6084, 6097, 6099 and XAC5010, trade names, available from CIBA-GEIGY (Japan) Limited; and alsoD.E.R. 660, 661, 662, 664, 667, 668 and 669, trade names, available fromDow Chemical Japan Ltd. Examples are by no means limited to these.

In particular, the thermosetting epoxy oligomer represented by Formula Vmust have an epoxy equivalent weight of from 400 to 6,000. Namely, if ithas an epoxy equivalent weight of less than 400, the amount of thethermosetting epoxy oligomer necessary for attaining a given viscositymust be increased when a photosensitive solution is prepared, to bringabout economical disadvantages, and also no bright holograms tend to beobtained since thermosetting epoxy oligomers may move to a certainextent at the time of fixing, because of its low molecular weight. Onthe other hand, a thermosetting epoxy oligomer having an epoxyequivalent weight of more than 6,000 usually makes it difficult to besynthesized in a stable molecular weight and a good reproducibility, andmakes the diffusibility of monomers poor, resulting in a lowering ofsensitivity and no bright holograms obtained. There is anotherdifficulty that no good cationic polymerization may proceed when it isoutside this range.

The aliphatic monomer being liquid at normal temperature and pressure,having a boiling point of 100° C. or above at normal pressure and beingcapable of radical polymerization has at least one ethylenicallyunsaturated bond in its structural unit, and includes monofunctionalvinyl monomers and besides polyfunctional vinyl monomers, or may bemixtures of these. It may specifically include high-boiling point vinylmonomers such as acrylic or methacrylic acid, itaconic acid, maleicacid, acryl- or methacrylamide, diacetone acrylamide and 2-hydroxyethylacrylate or methacrylate; aliphatic polyhydroxyl compounds asexemplified by di- or polyacrylic or methacrylic esters such as ethyleneglycol, diethylene glycol, triethylene glycol, tetraethylene glycol,propylene glycol, dipropylene glycol, tripropylene glycol,tetrapropylene glycol, neopentyl glycol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol,trimethylol propane, pentaerythritol, dipentaerythritol, sorbitol andmannitol; and alicyclic monomers such as dicyclopentanyl acrylate anddimethyloltricyclodecane diacrylate. Preferably it may include apolyethylene glycol diacrylate or dimethacrylate or polypropylene glycolacrylate or methacrylate represented by the following Formula VI:##STR10## wherein R₅ to R₇ each represent a hydrogen atom or a methylgroup; and m and n are each 0 or more and m+n is 1 to 20.

The first photoinitiator capable of simultaneously generating a radicalspecies that activates radical polymerization and a Br.o slashed.nstedacid or Lewis acid that activates cationic polymerization, upon exposureto actinic radiation, can be exemplified by the compounds disclosed inJ. Photopolym. Sci. Technol., 2, 283 (1989), and may specificallyinclude iron arene complexes, trihalogenomethyl-substituted s-triazines,sulfonium salts, diazonium salts, phosphonium salts, selenonium salts,arsonium salts and iodonium salts. The diaryliodonium salts may includethe compounds disclosed in Macromolecules, 10, 1307 (1977), asexemplified by chloride, bromide, tetrafluoroborate,hexafluorophosphate, hexafluoroarsenate, aromatic sulfonates or the likeof diphenyliodonium, ditolyliodonium, phenyl(p-anisyl)iodonium,bis(m-nitrophenyl)iodonium, bis(p-tert-butylphenyl)iodonium,bis(p-chlorophenyl)iodonium or the like.

As for the second photoinitiator comprised of a radical polymerizationphotoinitiator capable of generating a radical species that activatesradical polymerization upon exposure to actinic radiation and a cationicpolymerization photoinitiator capable of generating a Br.o slashed.nstedacid or Lewis acid that activates cationic polymerization upon exposureto actinic radiation, it can be exemplified by the following compounds.

The radical polymerization photoinitiator capable of generating aradical species that activates radical polymerization upon exposure toactinic radiation may include bisimidazole derivatives such as2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,1'-bisimidazole and(2,4,5-triphenyl)imidazole, N-arylglycine derivatives, and organic azidecompounds such as 4,4'-diazidochalcone, as well as titanocenes asdisclosed in Japanese Patent Application Laid-open No. 61-151197 andaluminato complexes disclosed in Japanese Patent Application Laid-openNo. 3-209477. Preferred radical polymerization photoinitiators mayinclude organic perroxides such as3,3',4',4-tetra(tert-butylperoxycarbonyl)benzophenone, andN-alkoxypyridinium salts such as 1-methoxy-4-phenylpyridiniumtetraphenyl borate. Without limitation to these examples, othercompounds may be used so long as the above properties are ensured.

The cationic polymerization photoinitiator capable of generating a Br.oslashed.nsted acid or Lewis acid that activates cationic polymerizationupon exposure to actinic radiation may include sulfonic esters,imidosulfonates, dialkyl-4-hydroxysulfonium salts,dialkyl-4-hydroxyphenylsulfonium salts, p-nitrobenzylarylsulfonates, andsilanol aluminum complexes. Examples thereof include benzoin tosylate,pyrogallol trimesylate, o-nitrobenzyl tosylate, 2,5-dinitrobenzyltosylate, N-tosylphthalimide, α-cyanobenzylidene tosylamine, andp-nitrobynzyl-9,10-diethoxyanthracene-2-sulfonate. Without limitation tothese examples, other compounds may be used so long as the aboveproperties are ensured.

The spectral sensitizer that sensitizes the first photoinitiator orsecond photoinitiator may include organic compounds such as cyanine ormerocyanine derivatives, coumarin derivatives, chalcone derivatives,xanthene derivatives, thioxanthene derivatives, azulenium derivatives,squatilium derivatives and porphyrin derivatives. Besides, the dyes andsensitizers as disclosed in Shinya Ohkawara et al., "SHIKISO HANDOBUKKU(Dye Handbook)", Kodansha Co., 1986; Shinya Ohkawara et al., "KINOUSEISIKISO NO KAGAKU (Chemistry of Functional Dyes)", CMC Co., 1981; andChuzaburo Ikemori et al., "TOKUSHU KINOU ZAIRYO (Special FunctionalMaterials)", CMC Co., 1981, may be used. Without limitation to thesecompounds, other dyes and sensitizers may be used so long as they canabsorb light of visible regions. Specific examples thereof are shownbelow.

As examples of cyanine or merocyanine derivatives, it is preferable touse, but without limitation to, Fluoresceine, Rhodamine,2,7-dichlorofluoresceine, 3,3'-dicarboxyethyl-2,2'-thiocyanine bromide,anhydro-3,3'-dicarboxyethyl-2,2'-thiocyanine betaine,1-carboxymethyl-1'-carboxyethyl-2,2'-quinocyanine bromide,anhydro-3,3'-dicarboxyethyl-5,5',9-trimethyl-2,2'-thiacarbocyaninebetaine, 3,3'-dihydroxyethyl-5,5'-dimethyl-9-ethyl-2,2'-thiacarbocyaninebromide, anhydro-3,3'-dicarboxymethyl-2,2'-thiocarbocyanine betaine, 2-3-ethyl-4-oxo-5-(1-ethyl-4-quinolinidene)-ethylidene-2-thiazolinidene-methyl!-3-ethylbenzoxazoliumbromide, 3-ethyl-5-2-(3-ethyl-2-benzothiazolinylidene)-ethylidene!rhodanine, 3-ethyl-5-2-(3-methyl-2(3H)-thiazolinylidene)-ethylidene!-2-thio-2,4-oxazolinedione,3-ethyl-5-(3-ethyl-benzothiazolinylidene)rhodanine,2-(p-diemthylaminostyryl)-3-ethylbenzothiazolium iodide,2-(p-diethylaminostyryl)-1-ethylpyridinium iodide, and1,3'-diethyl-2,2'-quinothiacyanine iodide.

As examples of coumarin derivatives, they may include, but are notlimited to, 3-(2'-benzimidazole)-7-N,N-diethylaminocoumarin,3,3'-carbonylbis(7-diethylaminocoumarin), 3,3'-carbonylbiscoumarin,3,3'-carbonylbis(7-methoxycoumarin),3,3'-carbonylbis(5,7-dimethoxycoumarin),3,3'-carbonylbis(6-methoxycoumarin),3,3'-carbonylbis(7-acetoxycoumarin),3,3'-carbonylbis(5,7-diisopropoxycoumarin),3,3'-carbonylbis(5,7-di-n-propoxycoumarin),3,3'-carbonylbis(5,7-di-n-butoxycoumarin),3,3'-carbonylbis(7-dimethyaminocoumarin),7-diethylamino-5',7'-dimethoxy-3,3'-carbonylbiscoumarin),3-benzoylcoumarin, 3-benzoyl-5,7-dimethoxycoumarin,3-benzoyl-6-methoxycoumarin, 3-benzoyl-7-methoxycoumarin,3-benzoyl-8-methoxycoumarin, 3-benzoyl-8-ethoxycoumarin,3-benzoyl-6-bromocoumarin, 3-benzoyl-7-dimethylaminocoumarin,3-benzoyl-7-diethylaminocoumarin, 3-benzoyl-7-hydroxycoumarin,3-acetyl-7-diethylaminocoumarin, 3-acetyl-7-methoxycoumarin,3-acetyl-5,7-dimethoxycoumarin,7-dimethylamino-3-(4-iodobenzoyl)coumarin,7-diethylamino-3-(4-iodobenzoyl)coumarin, and7-diethylamino-3-(4-diethylaminobenzoyl)coumarin.

As examples of chalcone derivatives, they may include, but are notlimited to, the following compounds. ##STR11##

As examples of porphyrin derivatives, it is preferable to use, butwithout limitation to, 9,10-dihydroporphyrin,5,9,15,10-tetramethylporphyrin,4,5,14,15-tetrahydro-4,9,14,19-tetramethyl-2,7,12,17-tetrazaporphyrin,meso-tetraphenylporphyrin, 4,5,9,10,14,15,19,20-octamethylporphyrin,5,9-diacetyl-4,10,14,15,19,20-hexamethylporphyrin,5,9-diacetyl-14-ethyl-4,10,15,19,20-pentamethylporphyrin,4,9,14,19-tetramethyl-5,10,15,20-tetrapropylporphyrin,2-amino-4,5,9,10,14,15,19,20-octaethylporphyrin,2-nitro-4,5,9,10,14,15,19,20-octaethylporphyrin,meso-diphenyltetrabenzoporphyrin,4,5-dibromo-9,10-,14,15-,19,20-tribenzo-2,7,12,17-tetrazaporphyrin,4,5,9,10,14,15,19,20-octaphenylporphyrin,tetrakis(3,4-dimethoxyphenyl)porphyrin,4,5,9,10,14,15,19,20-octa(p-methoxyphenyl)porphyrin, and copper, cobalt,nickel, zinc, platinum, magnesium or the like metal complexes thereof.

These spectral sensitizers may be selected so as to be adapted to thewavelengths of radiation sources serving as light sources, according tothe purposes for which holograms are used. Depending on their uses, twoor more kinds of them may be used in combination.

The photosensitive recording material may be further optionallyincorporated with known additives such as a heat polymerizationinhibitor, a chain transfer agent and an antioxidant.

The photosensitive recording material according to the present inventioncomprises, as described above, as main components the solvent-soluble,thermosetting epoxy oligomer capable of cationic polymerization; thealiphatic monomer having at least one ethylenically unsaturated bond,the monomer being liquid at normal temperature and pressure, having aboiling point of 100° C. or above at normal pressure and being capableof radical polymerization; the photoinitiator selected from the groupconsisting of i) the first photoinitiator capable of simultaneouslygenerating a radical species that activates radical polymerization and aBr.o slashed.nsted acid or Lewis acid that activates cationicpolymerization, upon exposure to actinic radiation, and ii) the secondphotoinitiator comprised of a radical polymerization photoinitiatorcapable of generating a radical species that activates radicalpolymerization upon exposure to actinic radiation and a cationicpolymerization photoinitiator capable of generating a Br.o slashed.nstedacid or Lewis acid that activates cationic polymerization upon exposureto actinic radiation; and the spectral sensitizer that sensitizes thefirst photoinitiator or second photoinitiator; where the aliphaticmonomer is mixed in an amount of from 20 to 80 parts by weight based on100 parts by weight of the thermosetting epoxy oligomer, which mayparticularly preferably be in an amount of from 40 to 70 parts byweight. If it is in an amount less than 20 parts by weight, the quantityof aliphatic monomers which undergo polymerization upon holographicexposure using a laser may become short and hence no high refractiveindex modulation can be obtained even after the heat treatment, makingit impossible to obtain bright holograms. If it is in an amount morethan 80 parts by weight, the quantity of aliphatic monomers may becomeexcess, so that no polymerization may take place upon the initialholographic exposure and aliphatic monomers may remain in the system ina large quantity. As the result, in the heat treatment in the productionsteps, the residual aliphatic monomers may cause polymerization whilediffusing, to disturb the interference fringes of holograms once formed,and hence no high refractive index modulation can be obtained to make itimpossible to obtain bright holograms.

The first photoinitiator or second photoinitiator may be used in anamount of from 0.1 to 20 parts by weight, and preferably from 1 to 10parts by weight, based on 100 parts by weight of the thermosetting epoxyoligomer. The spectral sensitizer may be used in an amount of from 0.1to 10 parts by weight, and preferably from 0.5 to 2 parts by weight,based on 100 parts by weight of the thermosetting epoxy oligomer. Theamount of these components is governed by the thickness of thephotosensitive layer formed and the optical density of that layer, andhence the amount may preferably be in such a range that the opticaldensity becomes not higher than 2. (Alternatively in terms oftransmittance, the amount may preferably be in such a range that thetransmittance of irradiation light at the photographing for hologramsbecomes not less than 1%.) If the amount is outside this range, itbecomes difficult to obtain a high diffraction efficiency, alsoresulting in a lowering of sensitivity characteristics.

Thus, these components are appropriately selected and mixed in thedesired proportions to obtain a photosensitive solution, which is thencoated in film on a substrate 2 such as a glass plate, a polycarbonateplate, a polymethyl methacrylate plate or a polyester film by a knowncoating means such as a spin coater, a roll coater or a bar coater toform a photosensitive layer 3. The product thus obtained is thephotosensitive recording medium, 1, used in the photographing ofholograms according to the present invention (see FIG. 2). On thephotosensitive layer 3, a protective layer 4 is further provided as anoxygen barrier layer. In the protective layer 4, the same material asthe substrate 2 or an optically transparent material, e.g., a plastic ofpolyolefin, polyvinyl chloride, polyvinylidene chloride, polyvinylalcohol or polyethylene terephthalate, or glass, is used, and the layeris superposed so as to hold the photosensitive layer between it and thesubstrate, or formed by lamination using an extruder or the like or bycoating a solution of such a material. When the photosensitive solutionis coated, the solution may be optionally diluted with a suitablesolvent. In such a case, after coated on the substrate, the coating mustbe dried. The photosensitive solution may also preferably be prepared inthe manner that the transmittance of photographing irradiation light maybe not less than 1%.

The solvent that can be used in the present invention is exemplified bydichloromethane, chloroform, acetone, 2-butanone, cyclohexanone, ethylacetate, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol,2-ethoxyethyl acetate, 2-butoxyethyl acetate, 2-methoxyethyl ether,2-ethoxyethyl ether, 2-(2-ethoxyethoxy)ethanol,2-(2-butoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethyl acetate,2-(2-butoxyethoxy)ethyl acetate, 1,4-dioxane and tetrahydrofuran.

FIG. 3 schematically illustrates a dual light flux optical system usedin the photographing for a hologram, where a laser beam 6 is shed from alaser 5, and is directed to the photosensitive recording medium 1 bymirrors 7 and a beam splitter 8 through spatial filters 9 and lenses 10.In the present invention, after the photographing for a hologram iscarried out by exposure, the fixing is carried out by a dry process. Thepresent invention can also be applied to the production of transmissionholograms, detailed description and illustration of which are hereinomitted, and a transmission hologram having a superior holographicperformance can be obtained.

When hologram images are recorded in this photosensitive recordingmedium 1, laser irradiation is applied in accordance with the desiredimages. More specifically, in the photosensitive layer (photosensitiverecording material) 3 of the photosensitive recording medium 1, thealiphatic monomers capable of radical polymerization and thesolvent-soluble, thermosetting epoxy oligomers capable of cationicpolymerization are uniformly distributed. In the hologram recording,upon exposure of this photosensitive layer 3 to laser interference light(i.e., light of the dual light flux optical system), the firstphotoinitiator or second photoinitiator in the photosensitive recordingmaterial of the photosensitive layer 3 simultaneously generates radicalspecies that activate radical polymerization and Br.o slashed.nsted acidor Lewis acid that activates cationic polymerization, at portionsundergoing a strong light interference action among laser irradiatedportions. The radical species generated here cause the aliphaticmonomers to undergo radical polymerization. As the monomers becomepolymerized, the photosensitive recording material causes differences indensity in the photosensitive layer 3, so that aliphatic monomers movefrom the neighborhood to those portions. That is, the density ofaliphatic monomers becomes higher at the portions undergoing a stronglight interference action among laser irradiated portions and thedensity thereof becomes lower at the portions undergoing a weak lightinterference action among laser irradiated portions. Thus, differencesin refractive index are produced between both the portions to effecthologram recording, as so presumed.

After the exposure to laser interference light, a heat treatment isfurther applied, whereupon the Br.o slashed.nsted acid or Lewis acidsimultaneously generated during the laser interference light irradiationacts to cause the solvent-soluble, thermosetting epoxy oligomer capableof cationic polymerization to undergo the cationic polymerizationaccording to light intensity distribution, so that presumably astructure with different crosslink density is formed and hence thiscontributes a more increase in the differences in refractive indexbetween the portions undergoing a strong light interference action andthe portions undergoing a weak light interference action among the laserirradiated portions, thus making it possible to obtain a volume typephase hologram having a high diffraction efficiency.

The thermosetting epoxy oligomer also serving as an image holding matrixturns to have a cross-linked structure attributable to the cationicpolymerization, so that the weatherability and chemical stability of theresulting volume type phase hologram can be improved.

Light sources in the step of interference pattern exposure, usable asthe light source suited for the photosensitive recording material of thepresent invention, include, but are not limited to, a helium cadmiumlaser, an argon laser, a krypton laser and a helium neon laser.

Thus, the photosensitive recording material according to the presentinvention can achieve in dry processing a superior sensitivity andresolution in visible light regions, because it comprises as maincomponents the solvent-soluble, thermosetting epoxy oligomer capable ofcationic polymerization; the aliphatic monomer having at least oneethylenically unsaturated bond, the monomer being liquid at normaltemperature and pressure, having a boiling point of 100° C. or above atnormal pressure and being capable of radical polymerization; thephotoinitiator selected from the group consisting of i) the firstphotoinitiator capable of simultaneously generating a radical speciesthat activates radical polymerization and a Br.o slashed.nsted acid orLewis acid that activates cationic polymerization, upon exposure toactinic radiation, and ii) the second photoinitiator comprised of aradical polymerization photoinitiator capable of generating a radicalspecies that activates radical polymerization upon exposure to actinicradiation and a cationic polymerization photoinitiator capable ofgenerating a Br.o slashed.nsted acid or Lewis acid that activatescationic polymerization upon exposure to actinic radiation; and thespectral sensitizer that sensitizes the first photoinitiator or secondphotoinitiator; where the aliphatic monomer is mixed in an amount offrom 20 to 80 parts by weight based on 100 parts by weight of thethermosetting epoxy oligomer.

Hence, the present invention has the advantage that a volume type phasehologram having superior diffraction efficiency, transparency andweatherability such as thermal resistance and being chemically stablecan be produced.

Since also the first photoinitiator or cationic polymerizationphotoinitiator highly effective for generating the Br.o slashed.nstedacid or Lewis acid is used in combination with the spectral sensitizer,the Br.o slashed.nsted acid or Lewis acid that acts when thethermosetting epoxy oligomer serving as an image holding matrix is madeto have a cross-linked structure can be generated in a higherefficiency, so that the diffraction efficiency of the volume type phasehologram after heating can be more improved.

Hence, the present invention has the advantage that it can be applied tophotosensitive recording materials suited for producing hologram opticaldevices required to have a very high performance.

The present invention will be still further described below in greaterdetail by giving Examples.

EXAMPLE 1

In 100 parts by weight of 2-butanone, 100 parts by weight of abisphenol-A type epoxy oligomer EPIKOTE 1007 (trade name; available fromYuka Shell Epoxy K.K.; degree of polymerization: n=10.8; epoxyequivalent weight: 1,750-2,100), 50 parts by weight of triethyleneglycol diacrylate, 5 parts by weight of diphenyliodoniumhexafluorophosphate and 1 part by weight of3,3'-carbonylbis(7-diethylaminocoumarin) were mixed and dissolved toobtain a photosensitive solution. This photosensitive solution wascoated on a glass plate so as to be in a layer thickness of about 15microns to form a photosensitive layer. Thereafter the surface of thephotosensitive layer was covered with a poly(vinyl alcohol) (PVA) filmto produce a photosensitive recording medium.

The photosensitive recording medium thus obtained was exposed to lightby means of the dual light flux optical system for hologramphotographing as shown in FIG. 3, using an argon laser (514.5 nm) as alight source, followed by heating at 100° C. for 30 minutes to produce ahologram.

The diffraction efficiency of the hologram thus obtained was measuredusing a spectrophotometer manufactured by Nihon Bunko Kogyo K.K. Thisspectrophotometer is so designed that a photomultimeter with a slit of 3mm wide can be placed on the area of 20 cm radius in circumferencearound a sample. The diffraction efficiency was measured by makingmonochromatic light with a beam width of 0.3 mm incident at an angle of45 degrees and detecting the light diffracted from the sample. The ratioof the greatest value other than those of specular reflected light tothe value measured when the incident light was directly received withoutplacing the sample was regarded as diffraction efficiency. Thediffraction efficiency before heating was also measured in the samemanner. The results of evaluation of diffraction efficiency are shown inTable 1. In the table, "D.E." and "R.I.C." represent diffractionefficiency and refractive index modulation, respectively.

EXAMPLES 2 to 6

The procedure of Example 1 was repeated to produce holograms except thatthe triethylene glycol diacrylate (TEGDA) was replaced with diethyleneglycol diacrylate (DEGDA), neopentyl glycol diacrylate (NPGDA),ethylcarbitol acrylate (EKA), 1,6-hexanediol diacrylate (HDDA) andtriethylene glycol dimethacrylate (TEGDMA), respectively. Thediffraction efficiency was also measured similarly. Results of theevalution are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                 Amount Layer  Before     After                                                of expo-                                                                             thick- heating    heating                                     Ex-   Aliphatic                                                                              sure     ness D.E. R.I.C.                                                                              D.E. R.I.C.                           ample:                                                                              monomer  (mJ/cm.sup.2)                                                                          (μm)                                                                            (%)  (×100)                                                                        (%)  (×100)                     ______________________________________                                        1     TEGDA    20       15.1 12.5 0.40  75.4 1.44                             2     DEGDA    20       17.0 25.0 0.53  89.2 1.71                             3     NPGDA    20       13.1 8.7  0.38  71.9 1.56                             4     EKA      20       14.5 10.0 0.37  77.7 1.56                             5     HDDA     20       15.7 15.2 0.43  81.3 1.54                             6     TEGDMA   20       16.2 16.1 0.43  87.1 1.71                             ______________________________________                                    

D.E. and R.I.C. represent diffraction efficiency and refractive indexmodulation, respectively.

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

EXAMPLES 7 to 12

The procedure of Example 1 was repeated to produce holograms except thatthe bisphenol-A type epoxy oligomer EPIKOTE 1007 (trade name; availablefrom Yuka Shell Epoxy K.K.; degree of polymerization: n=10.8; epoxyequivalent weight: 1,750-2,100) used therein was replaced with EPIKOTE1001 (EP-1001; trade name; available from Yuka Shell Epoxy K.K.; degreeof polymerization: n=2.4; epoxy equivalent weight: 450-500), EPIKOTE1004 (EP-1004; trade name; available from Yuka Shell Epoxy K.K.; degreeof polymerization: n=4.5; epoxy equivalent weight: 900-1,000), EPIKOTE1009 (EP-1009; trade name; available from Yuka Shell Epoxy K.K.; degreeof polymerization: n=14.3; epoxy equivalent weight: 2,400-3,000),ARALDITE 6071 (AR-6071; trade name; available from CIBA-GEIGY (Japan)Limited; degree of polymerization: n=2.4; epoxy equivalent weight:450-500), ARALDITE 6099 (AR-6099; trade name; available from CIBA-GEIGY(Japan) Limited; degree of polymerization: n=14.3; epoxy equivalentweight: 2,400-3,300) and D.E.R. 668 (DER-668; trade name; available fromDow Chemical Japan Ltd.; degree of polymerization: n=12.5; epoxyequivalent weight: 2,000-3,500), respectively. The diffractionefficiency was also measured similarly. Results of the evalution areshown in Table 2.

                  TABLE 2                                                         ______________________________________                                                 Amount Layer  Before     After                                                of expo-                                                                             thick- heating    heating                                     Ex-   Epoxy    sure     ness D.E. R.I.C.                                                                              D.E. R.I.C.                           ample:                                                                              oligomer (mJ/cm.sup.2)                                                                          (μm)                                                                            (%)  (×100)                                                                        (%)  (×100)                     ______________________________________                                        7     EP-1001  20       15.3 14.9 0.44  83.5 1.66                             8     EP-1004  20       17.4 15.3 0.38  92.3 1.84                             9     EP-1009  20       17.1 23.1 0.50  82.1 1.44                             10    AR-6071  20       15.7 15.2 0.37  81.3 1.54                             11    AR-6099  20       19.3 30.0 0.52  88.1 1.46                             12    DER-668  20       15.2 15.8 0.45  85.7 1.75                             ______________________________________                                    

D.E. and R.I.C. represent diffraction efficiency and refractive indexmodulation, respectively.

EP-1001: EPIKOTE 1001, Yuka Shell Epoxy K.K.

EP-1004: EPIKOTE 1004, Yuka Shell Epoxy K.K.

EP-1009: EPIKOTE 1009, Yuka Shell Epoxy K.K.

AR-6071: ARALDITE 6071, CIBA-GEIGY (Japan) Limited

AR-6099: ARALDITE 6099, CIBA-GEIGY (Japan) Limited

DER-668: D.E.R. 668, Dow Chemical Japan Ltd.

EXAMPLES 13 to 18

The procedure of Example 1 was repeated to produce holograms except thatthe spectral sensitizer 3,3'-carbonylbis(7-diethylaminocoumarin) usedtherein was replaced with2-benzoyl-3-(p-dimethylaminophenyl)-2-propenenitrile. The diffractionefficiency was also measured similarly. Results of the evalution areshown in Table 3. At the time of exposure, the argon laser of 514.5 nmwas replaced with that of 488 nm.

                  TABLE 3                                                         ______________________________________                                                 Amount Layer  Before     After                                                of expo-                                                                             thick- heating    heating                                     Ex-   Aliphatic                                                                              sure     ness D.E. R.I.C.                                                                              D.E. R.I.C.                           ample:                                                                              monomer  (mJ/cm.sup.2)                                                                          (μm)                                                                            (%)  (×100)                                                                        (%)  (×100)                     ______________________________________                                        13    TEGDA    30       15.5 14.5 0.40  72.7 1.27                             14    DEGDA    30       14.3 20.0 0.52  81.5 1.62                             15    NPGDA    30       16.7 12.7 0.35  74.0 1.20                             16    EKA      30       14.6 11.6 0.38  73.2 1.36                             17    HDDA     30       16.3 14.2 0.38  81.3 1.41                             18    TEGDMA   30       15.1 18.1 0.47  82.1 1.55                             ______________________________________                                    

D.E. and R.I.C. represent diffraction efficiency and refractive indexmodulation, respectively.

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

EXAMPLES 19 to 24

The procedure of Example 1 was repeated to produce holograms except thatthe spectral sensitizer 3,3'-carbonylbis(7-diethylaminocoumarin) usedtherein was replaced with 3-ethyl-5- 2-(3-ethyl-2-benzothiazolinylidene.The diffraction efficiency was also measured similarly. Results of theevalution are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                                 Amount Layer  Before     After                                                of expo-                                                                             thick- heating    heating                                     Ex-   Aliphatic                                                                              sure     ness D.E. R.I.C.                                                                              D.E. R.I.C.                           ample:                                                                              monomer  (mJ/cm.sup.2)                                                                          (μm)                                                                            (%)  (×100)                                                                        (%)  (×100)                     ______________________________________                                        19    TEGPA    30       14.3 15.2 0.45  75.3 1.44                             20    DEGDA    30       15.3 16.6 0.44  82.3 1.53                             21    NPGDA    30       15.7 14.0 0.39  77.1 1.35                             22    EKA      30       13.8 13.2 0.43  70.1 1.36                             23    HDDA     30       14.5 15.0 0.44  81.2 1.58                             24    TEGDMA   30       14.7 16.1 0.45  79.2 1.50                             ______________________________________                                    

D.E. and R.I.C. represent diffraction efficiency and refractive indexmodulation, respectively.

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

The holograms according to Examples 1 to 24 caused no lowering ofdiffraction efficiency even after they were left in an environment of25° C., 60% RH for 180 days and in an environment of 150° C. for 10hours.

Comparative Examples 1 to 3

The procedure of Example 1 was repeated to produce holograms except thatthe bisphenol-A type epoxy oligomer EPIKOTE 1007 (trade name; availablefrom Yuka Shell Epoxy K.K.; degree of polymerization: n=10.8; epoxyequivalent weight: 1,750-2,100) used therein was replaced with EPIKOTE828 (EP-828; trade name; available from Yuka Shell Epoxy K.K.; degree ofpolymerization: n=0.23; epoxy equivalent weight: 184-194), ARALDITEGY280 (AR-GY280; trade name; available from CIBA-GEIGY (Japan) Limited;degree of polymerization: n=0.76; epoxy equivalent weight: 225-280) andEPIKOTE 1255HX30 (EP-1255; trade name; available from Yuka Shell EpoxyK.K.; degree of polymerization: n>40; epoxy equivalent weight: 10,000 ormore; containing 35% by weight each of n-hexane and xylene),respectively. The diffraction efficiency was also measured similarly.Results of the evalution are shown in Table 5.

    ______________________________________                                                        Amount                                                        Com-            of expo-                                                                              Layer                                                                              Before   After                                   parative        sure    thick-                                                                             heating  heating                                 Ex-   Epoxy     (mJ/    ness D.E. R.I.C.                                                                              D.E. R.I.C.                           ample:                                                                              oligomer  cm.sup.2)                                                                             (μm)                                                                            (%)  (×100)                                                                        (%)  (×100)                     ______________________________________                                        1     EP-828    30      15.7 11.1 0.36  12.3 0.38                             2     AR-GY280  30      14.3 12.2 0.42  13.8 0.45                             3     EP1255    30      15.3 8.6  0.32  9.0  0.33                             ______________________________________                                    

D.E. and R.I.C. represent diffraction efficiency and refractive indexmodulation, respectively.

AR-GY280: ARALDITE GY280, CIBA-GEIGY (Japan) Limited

EP-828: EPIKOTE 828, Yuka Shell Epoxy K.K.

EP-1255: EPIKOTE 1255HX30, Yuka Shell Epoxy K.K.

In these Comparative Examples, the degree of polymerization n was lessthan 1 or more than 20. Hence, as shown in Table 5, it was ascertainedthat the diffraction efficiency of each hologram obtained was inferiorto that of Examples.

Comparative Examples 4, 5

The procedure of Example 1 was repeated to produce holograms except thatthe triethylene glycol diacrylate (the aliphatic monomer) used thereinwas replaced with an aromatic monomer phenoxyethyl acrylate VISCOAT #192(trade name; available from Osaka Organic Chemical Ind. Co., Ltd.) andbenzyl acrylate VISCOAT #160 (trade name; available from Osaka OrganicChemical Ind. Co., Ltd.), respectively.

However, since no aliphatic monomer was used, no hologram was produciblein either case.

Comparative Examples 6, 7

The procedure of Example 2 was repeated to produce holograms except thatthe diethylene glycol diacrylate used therein was added in an amount of10 or 100 parts by weight (pbw) based on 100 parts by weight of thebisphenol-A type epoxy oligomer EPIKOTE 1007. The diffraction efficiencywas also measured similarly. Results of the evalution are shown in Table6.

    ______________________________________                                        Com-           Amount   Layer                                                                              Before   After                                   parative                                                                            Epoxy    of expo- thick-                                                                             heating  heating                                 Ex-   oligomer sure     ness D.E. R.I.C.                                                                              D.E. R.I.C.                           ample:                                                                              EP-1007  (mJ/cm.sup.2)                                                                          (μm)                                                                            (%)  (×100)                                                                        (%)  (×100)                     ______________________________________                                        6      10 pbw  30       16.2 9.2  0.32  Hologram                                                                      disappeared                           7     100 pbw  30       16.5 12.1 0.36  14.2 0.39                             ______________________________________                                    

D.E. and R.I.C. represent diffraction efficiency and refractive indexmodulation, respectively.

Since, however, in each Comparative Example the mixing proportion of thealiphatic monomer based on 100 parts by weight of the thermosettingepoxy oligomer was not set within the range of 20 to 80 parts by weight,it turned out that, as shown in Table 6, in Comparative Example 6 thehologram disappeared after the heating, and in Comparative Example 7 thehologram showed an inferior diffraction efficiency.

Comparative Examples 8 to 13

The procedures of Examples 1 to 6 were respectively repeated to produceholograms except that, after the photosensitive recording mediums wereexposed by means of the dual light flux optical system using the argonlaser (514.5 nm) as a light source, they were each subjected to overallexposure using a high-pressure mercury lamp under conditions of 100mJ/cm², followed by the heat treatment at 100° C. for 30 minutes. Thediffraction efficiency was also measured similarly. Results of theevalution are shown in Table 7. It was ascertained from the results thatas previously stated, when the exposure to ultraviolet rays or otheractinic radiations was carried out before the heat treatment, theheat-curing of epoxy brought about no improvement in diffractionefficiency.

                  TABLE 7                                                         ______________________________________                                        Com-           Amount   Layer                                                                              Before   After                                   parative       of expo- thick-                                                                             heating  heating                                 Ex-   Aliphatic                                                                              sure     ness D.E. R.I.C.                                                                              D.E. R.I.C.                           ample:                                                                              monomer  (mJ/cm.sup.2)                                                                          (μm)                                                                            (%)  (×100)                                                                        (%)  (×100)                     ______________________________________                                        8     TEGDA    20       14.1 12.0 0.42  13.2 0.44                             9     DEGDA    20       15.3 17.7 0.48  18.1 0.49                             10    NPGDA    20       15.7 14.0 0.41  13.7 0.41                             11    EKA      20       13.5 8.8  0.37  10.1 0.40                             12    HDDA     20       14.8 14.3 0.44  14.8 0.45                             13    TEGDMA   20       15.2 14.4 0.43  16.1 0.46                             ______________________________________                                    

D.E. and R.I.C. represent diffraction efficiency and refractive indexmodulation, respectively.

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

Comparative Example 14

In 100 parts by weight of hydroxypropyl acrylate and 25 parts by weightof 2-butanone, 35 parts by weight of a bisphenol-A type epoxy oligomerEPIKOTE 1001 (EP-1001; trade name; available from Yuka Shell Epoxy K.K.;degree of polymerization: n=2.4; epoxy equivalent weight: 450-500) and14 parts by weight of an epoxy curing agent FUJICURE FXR-1030 (tradename; available from Fuji Kasei Co., Ltd.) were dissolved to obtain asolution, to which 5 parts by weight of3,3',4,4'-tetra(tert-butylperoxycarbonyl)benzophenone and 0.2 part byweight of 3,3'-carbonylbis(7-diethylaminocuramrine) were further addedto obtain a photosensitive solution. This photosensitive solution washeld between two sheets of transparent glass plates to form aphotosensitive layer with a layer thickness of 19.5 μm. Thephotosensitive layer thus obtained was irradiated with ultraviolet raysto carry out pre-polymerization until the layer becomes non-fluid,followed by holographic exposure in the same manner as in Example 1, andalso subjected to overall irradiation with ultraviolet rays, followed byheating at 80° C. for 30 hours. As a result, a hologram with adiffraction efficiency of 35.6% (refractive index modulation: 0.0058)was obtained.

On account of such hologram characteristic values (diffractionefficiency: 35.6%; refractive index modulation: 0.0058), it wasascertained that the compositional proportions of materials andproduction process as disclosed in Japanese Patent Application Laid-openNo. 5-94014 could not provide such bright holograms as in Examples ofthe present invention.

Comparative Example 15

In 100 parts by weight of hydroxypropyl acrylate, 50 parts by weight ofa cationic polymerization type ultraviolet-curable epoxy resin OPTOMERKR-600 (trade name; available from Asahi Denka Kogyo K.K.) was dissolvedto obtain a solution, to which 5 parts by weight of3,3',4,4'-tetra(tert-butylperoxycarbonyl)benzophenone and 0.2 part byweight of 3,3'-carbonylbis(7-diethylaminocuramrine) were further addedto obtain a photosensitive solution.

The subsequent steps of Comparative Example 14 were followed to form aphotosensitive layer, which was then subjected to the pre-exposure andthe holographic exposure, followed by the overall irradiation withultraviolet rays. As a result, a hologram with a diffraction efficiencyof 42.3% (refractive index modulation: 0.0063; layer thickness: 20.3 μm)was obtained.

On account of such hologram characteristic values (diffractionefficiency: 42.3%; refractive index modulation: 0.0063), it wasascertained that the compositional proportions of materials andproduction process as disclosed in Japanese Patent Application Laid-openNo. 5-94014 could not provide the bright holograms as in Examples of thepresent invention.

EXAMPLE 25

In 100 parts by weight of 2-butanone, 100 parts by weight of athermosetting epoxy oligomer (bisphenol-S type; trade name: EBPS300;available from Nippon Kayaku Co., Ltd.), 50 parts by weight oftriethylene glycol diacrylate, 5 parts by weight of diphenyliodoniumhexafluorophosphate and 1 part by weight of3,3'-carbonylbis(7-diethylaminocoumarin) were mixed and dissolved toobtain a photosensitive solution. This photosensitive solution wascoated on a glass plate by means of an applicator so as to be in athickness of about 15 microns to form a photosensitive layer. Thereafterthe surface of the photosensitive layer was covered with a poly(vinylalcohol) (PVA) film to produce a photosensitive recording mediumaccording to the present Example.

The photosensitive recording medium thus obtained was exposed to lightby means of the dual light flux optical system for hologramphotographing as shown in FIG. 3, using an argon laser (514.5 nm) as alight source, to form a hologram image, followed by heating at 100° C.for 30 minutes to obtain a hologram.

The diffraction efficiency of the hologram thus obtained was measured inthe same manner as in Example 1. The diffraction efficiency before theheating was also measured similarly. Results of the evaluation are shownin Table 8.

EXAMPLES 26 to 30

The procedure of Example 25 was repeated to produce holograms exceptthat the triethylene glycol diacrylate (TEGDA) was replaced withdiethylene glycol diacrylate (DEGDA), neopentyl glycol diacrylate(NPGDA), ethylcarbitol acrylate (EKA), 1,6-hexanediol diacrylate (HDDA)and triethylene glycol dimethacrylate (TEGDMA), respectively. Thediffraction efficiency was also measured similarly. The diffractionefficiency before the heating was also measured similarly. Results ofthe evalution are shown in Table 8.

                  TABLE 8                                                         ______________________________________                                                     Amount of                                                        Aliphatic    exposure  Diffraction efficiency (%)                             Example:                                                                              monomer  (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        25      TEGDA    20        15.0     81.2                                      26      DEGDA    20        26.7     88.0                                      27      NPGDA    20        15.2     78.6                                      28      EKA      20        16.8     79.2                                      29      HDDA     20        18.0     80.9                                      30      TEGDMA   20        21.6     85.0                                      ______________________________________                                    

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

EXAMPLES 31 TO 36

The procedure of Examples 25 to 30 each was repeated to produceholograms except that the thermosetting epoxy oligomer (trade name:EBPS300; available from Nippon Kayaku Co., Ltd.) used therein wasreplaced with a thermosetting epoxy oligomer ARALDITE PY306 (trade name;available from CIBA-GEIGY (Japan) Limited) to prepare photosensitivesolutions, which were then each held between two sheets of glass plates.The diffraction efficiency was also measured similarly. The diffractionefficiency before the heating was also measured similarly. Results ofthe evalution are shown in Table 9.

                  TABLE 9                                                         ______________________________________                                                     Amount of                                                        Aliphatic    exposure  Diffraction efficiency (%)                             Example:                                                                              monomer  (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        31      TEGDA    20        10.5     71.0                                      32      DEGDA    20        18.2     79.6                                      33      NPGDA    20         6.5     68.5                                      34      EKA      20         9.2     70.2                                      35      HDDA     20        13.8     76.2                                      36      TEGDMA   20        17.3     78.6                                      ______________________________________                                    

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

EXAMPLES 37 TO 42

The procedure of Examples 31 to 36 each was repeated to produceholograms except that the thermosetting epoxy oligomer (trade name:ARALDITE PY306; available from CIBA-GEIGY (Japan) Limited) used thereinwas replaced with a thermosetting epoxy oligomer R-710 (trade name;available from Mitsui Petrochemical Industries, Ltd.). The diffractionefficiency was also measured similarly. The diffraction efficiencybefore the heating was also measured similarly. Results of the evalutionare shown in Table 10.

                  TABLE 10                                                        ______________________________________                                                     Amount of                                                        Aliphatic    exposure  Diffraction efficiency (%)                             Example:                                                                              monomer  (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        Example:                                                                      37      TEGDA    20        11.7     76.1                                      38      DEGDA    20        21.0     86.2                                      39      NPGDA    20        10.6     71.2                                      40      EKA      20        12.6     74.9                                      41      HDDA     20        12.1     78.6                                      42      TEGDMA   20        18.3     81.8                                      ______________________________________                                    

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

EXAMPLES 43 TO 45

The procedure of Example 25 was repeated to produce holograms exceptthat, the thermosetting epoxy oligomer (trade name: EBPS300; availablefrom Nippon Kayaku Co., Ltd.) used therein was replaced with 100 partsby weight a novolak type thermosetting epoxy oligomer (trade name:EPPN-201; available from Nippon Kayaku Co., Ltd.), a brominated novolaktype thermosetting epoxy oligomer (trade name: BREN-S; available fromNippon Kayaku Co., Ltd.) and an o-cresol novolak type thermosettingepoxy oligomer (trade name: EOCN-104; available from Nippon Kayaku Co.,Ltd.), respectively, and the components were dissolved in 100 parts byweight of methyl ethyl ketone to obtain photosensitive solutions. Thediffraction efficiency was also measured similarly. The diffractionefficiency before the heating was also measured similarly. Results ofthe evalution are shown in Table 11.

                  TABLE 11                                                        ______________________________________                                        Thermo-                                                                       setting      Amount of                                                        epoxy        exposure  Diffraction efficiency (%)                             Example:                                                                              oligomer (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        43      EPPN-201 20        15.0     81.2                                      44      BREN-S   20        26.7     88.0                                      45      EOCN-    20        15.2     78.6                                              104                                                                   ______________________________________                                    

EXAMPLES 46 TO 51

The procedure of Example 25 to 30 each was repeated to produce hologramsexcept that the spectral sensitizer3,3'-carbonylbis(7-diethylaminocoumarin) used therein was replaced with2-benzoyl-3-(p-dimethylaminophenyl)-2-propenenitrile. The diffractionefficiency was also measured similarly. The diffraction efficiencybefore the heating was also measured similarly. Results of the evalutionare shown in Table 12. At the time of exposure, the argon laser of 514.5nm was replaced with that of 488 nm.

                  TABLE 12                                                        ______________________________________                                                     Amount of                                                        Aliphatic    exposure  Diffraction efficiency (%)                             Example:                                                                              monomer  (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        46      TEGDA    30         8.2     65.0                                      47      DEGDA    30        15.7     74.3                                      48      NPGDA    30         5.9     65.2                                      49      EKA      30         8.1     67.3                                      50      HDDA     30        11.6     70.6                                      51      TEGDMA   30        15.3     71.7                                      ______________________________________                                    

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

The holograms according to Examples 25 to 51 caused no lowering ofdiffraction efficiency even after they were left in an environment of25° C., 60% RH for 180 days and in an environment of 150° C. for 10hours.

EXAMPLE 52

In 100 parts by weight of 2-butanone, 100 parts by weight of abisphenol-A type epoxy oligomer EPIKOTE 1007 (trade name; available fromYuka Shell Epoxy K.K.; degree of polymerization: n=10.8; epoxyequivalent weight: 1,750-2,100), 50 parts by weight of triethyleneglycol diacrylate, 5 parts by weight of an iron arene complex(hexafluorophosphate) and 1 part by weight of3,3'-carbonylbis(7-diethylaminocoumarin) were mixed and dissolved toobtain a photosensitive solution. This photosensitive solution wascoated on a glass plate so as to be in a layer thickness of about 15microns to form a photosensitive layer. Thereafter the surface of thephotosensitive layer was covered with a poly(vinyl alcohol) (PVA) filmto produce a photosensitive recording medium.

The photosensitive recording medium thus obtained was exposed to lightby means of the dual light flux optical system for hologramphotographing as shown in FIG. 3, using an argon laser (488 nm) as alight source, followed by heating at 100° C. for 30 minutes to obtain ahologram.

The diffraction efficiency of the hologram thus obtained was measured inthe same manner as in Example 1. The diffraction efficiency before theheating was also measured similarly. Results of the evaluation are shownin Table 13.

EXAMPLES 53 TO 57

The procedure of Example 52 was repeated to produce holograms exceptthat the triethylene glycol diacrylate (TEGDA) was replaced withdiethylene glycol diacrylate (DEGDA), neopentyl glycol diacrylate(NPGDA), ethylcarbitol acrylate (EKA), 1,6-hexanediol diacrylate (HDDA)and triethylene glycol dimethacrylate (TEGDMA), respectively. Thediffraction efficiency was also measured similarly. The diffractionefficiency before the heating was also measured similarly. Results ofthe evalution are shown in Table 13.

                  TABLE 13                                                        ______________________________________                                                     Amount of                                                        Aliphatic    exposure  Diffraction efficiency (%)                             Example:                                                                              monomer  (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        52      TEGDA    25        10.2     71.7                                      53      DEGDA    25        17.5     81.6                                      54      NPGDA    25         7.8     69.2                                      55      EKA      25         8.4     69.0                                      56      HDDA     25        11.9     74.9                                      57      TEGDMA   25        19.6     77.7                                      ______________________________________                                    

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

EXAMPLES 58 TO 63

The procedure of Example 52 was repeated to produce holograms exceptthat the bisphenol-A type epoxy oligomer EPIKOTE 1007 (trade name;available from Yuka Shell Epoxy K.K.; degree of polymerization: n=10.8;epoxy equivalent weight: 1,750-2,100) used therein was replaced withEPIKOTE 1001 (EP-1001; trade name; available from Yuka Shell Epoxy K.K.;degree of polymerization: n=2.4; epoxy equivalent weight: 450-500),EPIKOTE 1004 (EP-1004; trade name; available from Yuka Shell Epoxy K.K.;degree of polymerization: n=4.5; epoxy equivalent weight: 900-1,000),EPIKOTE 1009 (EP-1009; trade name; available from Yuka Shell Epoxy K.K.;degree of polymerization: n=14.3; epoxy equivalent weight: 2,400-3,000),ARALDITE 6071 (AR-6071; trade name; available from CIBA-GEIGY (Japan)Limited; degree of polymerization: n=2.4; epoxy equivalent weight:450-500), ARALDITE 6099 (AR-6099; trade name; available from CIBA-GEIGY(Japan) Limited; degree of polymerization: n=14.3; epoxy equivalentweight: 2,400-3,300) and D.E.R. 668 (DER-668; trade name; available fromDow Chemical Japan Ltd.; degree of polymerization: n=12.5; epoxyequivalent weight: 2,000-3,500), respectively. The diffractionefficiency was also measured similarly. Results of the evalution areshown in Table 14.

                  TABLE 14                                                        ______________________________________                                        Thermo-                                                                       setting      Amount of                                                        epoxy        exposure  Diffraction efficiency (%)                             Example:                                                                              oligomer (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        58      EP-1001  20        11.7     76.1                                      59      EP-1004  20        21.0     86.5                                      60      EP-1009  20        10.6     71.2                                      61      AR-6071  20        12.6     74.9                                      62      AR-6099  20        12.1     78.6                                      63      DER-668  20        18.3     81.8                                      ______________________________________                                    

EP-1001: EPIKOTE 1001, Yuka Shell Epoxy K.K.

EP-1004: EPIKOTE 1004, Yuka Shell Epoxy K.K.

EP-1009: EPIKOTE 1009, Yuka Shell Epoxy K.K.

AR-6071: ARALDITE 6071, CIBA-GEIGY (Japan) Limited

AR-6099: ARALDITE 6099, CIBA-GEIGY (Japan) Limited

DER-668: D.E.R. 668, Dow Chemical Japan Ltd.

EXAMPLES 64 TO 69

The procedure of Examples 52 to 57 each was repeated to produceholograms except that the photoinitiator iron arene complex(hexafluorophosphate) used in Example 52 was replaced with1,3,5-trichloromethyltriazine. The diffraction efficiency was alsomeasured similarly. The diffraction efficiency before the heating wasalso measured similarly. Results of the evalution are shown in Table 15.

                  TABLE 15                                                        ______________________________________                                                     Amount of                                                        Aliphatic    exposure  Diffraction efficiency (%)                             Example:                                                                              monomer  (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        64      TEGDA    20        10.2     72.3                                      65      DEGDA    20        14.3     84.2                                      66      NPGDA    20         9.5     71.0                                      67      EKA      20         8.7     68.4                                      68      HDDA     20        10.5     75.0                                      69      TEGDMA   20        18.0     75.3                                      ______________________________________                                    

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

EXAMPLES 70 TO 74

The procedure of Example 53 was repeated to produce holograms exceptthat the spectral sensitizer 3,3'-carbonylbis(7-diethylaminocoumarin)used therein was replaced with Rose Bengale (RB),4,4'-dimethylaminochalcone (DMAC), 4,4'-bis(dimethylamino)benzalacetone(BDMABA), 3,3'-diethyl-2,2'-oxacarbocyanine iodide (DEOCCI) and2,4,6-triphenylthiapyrylium perchlorate (TPTPPC), respectively. Thediffraction efficiency was also measured similarly. The diffractionefficiency before the heating was also measured similarly. Results ofthe evalution are shown in Table 16. At the time of exposure, the argonlaser of 514.5 nm was replaced with that of 488 nm.

                  TABLE 16                                                        ______________________________________                                                     Amount of                                                                     exposure  Diffraction efficiency (%)                             Example:                                                                              Sensitizer                                                                             (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        70      RB       30        8.2      65.0                                      71      DMAC     30        15.7     74.3                                      72      BDMABA   30        5.9      65.2                                      73      DEOCCI   30        8.1      67.3                                      74      TPTPPC   30        11.6     70.6                                      ______________________________________                                    

RB: Rose Bengale

DMAC: 4,4'-Dimethylaminochalcone

BDMABA: 4,4'-Bis(dimethylamino)benzalacetone

DEOCCI: 3,3'-Diethyl-2,2'-oxacarbocyanine iodide

TPTPPC: 2,4,6-Triphenylthiapyrylium perchlorate

The holograms according to Examples 52 to 74 also caused no lowering ofdiffraction efficiency even after they were left in an environment of25° C., 60% RH for 180 days and in an environment of 150° C. for 10hours.

EXAMPLE 75

In 100 parts by weight of 2-butanone, 100 parts by weight of abisphenol-A type epoxy oligomer EPIKOTE 1007 (trade name; available fromYuka Shell Epoxy K.K.; degree of polymerization: n=10.8; epoxyequivalent weight: 1,750-2,100), 50 parts by weight of triethyleneglycol diacrylate, 5 parts by weight of2,2',5,5'-tetra(tert-butylperoxycarbonyl)benzophenone (a radicalpolymerization photoinitiator), 3 parts by weight ofp-nitrobenzyl-9,10-dianthacene-2-sulfonate (cationic polymerizationphotoinitiator) and 1 part by weight of3,3'-carbonylbis(7-diethylaminocoumarin) were mixed and dissolved toobtain a photosensitive solution. This photosensitive solution wascoated on a glass plate so as to be in a layer thickness of about 15microns to form a photosensitive layer. Thereafter the surface of thephotosensitive layer was covered with a poly(vinyl alcohol) (PVA) filmto produce a photosensitive recording medium.

The photosensitive recording medium thus obtained was exposed to lightby means of the dual light flux optical system for hologramphotographing as shown in FIG. 3, using an argon laser (488 nm) as alight source, followed by heating at 100° C. for 30 minutes to obtain ahologram.

The diffraction efficiency of the hologram thus obtained was measured inthe same manner as in Example 1. The diffraction efficiency before theheating was also measured similarly. Results of the evaluation are shownin Table 17.

EXAMPLES 76 TO 80

The procedure of Example 75 was repeated to produce holograms exceptthat the triethylene glycol diacrylate (TEGDA) was replaced withdiethylene glycol diacrylate (DEGDA), neopentyl glycol diacrylate(NPGDA), ethylcarbitol acrylate (EKA), 1,6-hexanediol diacrylate (HDDA)and triethylene glycol dimethacrylate (TEGDMA), respectively. Thediffraction efficiency was also measured similarly. The diffractionefficiency before the heating was also measured similarly. Results ofthe evalution are shown in Table 17.

                  TABLE 17                                                        ______________________________________                                                     Amount of                                                        Aliphatic    exposure  Diffraction efficiency (%)                             Example:                                                                              monomer  (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        75      TEGDA    25        10.1     70.2                                      76      DEGDA    25        16.2     83.6                                      77      NPGDA    25         5.9     64.5                                      78      EKA      25         8.9     66.2                                      79      HDDA     25        10.9     72.6                                      80      TEGDMA   25        17.2     74.9                                      ______________________________________                                    

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

EXAMPLES 81 TO 86

The procedure of Example 75 was repeated to produce holograms exceptthat the bisphenol-A type epoxy oligomer EPIKOTE 1007 (trade name;available from Yuka Shell Epoxy K.K.; degree of polymerization: n=10.8;epoxy equivalent weight: 1,750-2,100) used therein was replaced withEPIKOTE 1001 (EP-1001; trade name; available from Yuka Shell Epoxy K.K.;degree of polymerization: n=2.4; epoxy equivalent weight: 450-500),EPIKOTE 1004 (EP-1004; trade name; available from Yuka Shell Epoxy K.K.;degree of polymerization: n=4.5; epoxy equivalent weight: 900-1,000),EPIKOTE 1009 (EP-1009; trade name; available from Yuka Shell Epoxy K.K.;degree of polymerization: n=14.3; epoxy equivalent weight: 2,400-3,000),ARALDITE 6071 (AR-6071; trade name; available from CIBA-GEIGY (Japan)Limited; degree of polymerization: n=2.4; epoxy equivalent weight:450-500), ARALDITE 6099 (AR-6099; trade name; available from CIBA-GEIGY(Japan) Limited; degree of polymerization: n=14.3; epoxy equivalentweight: 2,400-3,300) and D.E.R. 668 (DER-668; trade name; available fromDow Chemical Japan Ltd.; degree of polymerization: n=12.5; epoxyequivalent weight: 2,000-3,500), respectively. The diffractionefficiency was also measured similarly. Results of the evalution areshown in Table 18.

                  TABLE 18                                                        ______________________________________                                        Thermo-                                                                       setting      Amount of                                                        epoxy        exposure  Diffraction efficiency (%)                             Example:                                                                              oligomer (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        81      EP-1001  20         9.9     72.1                                      82      EP-1004  20        16.3     79.0                                      83      EP-1009  20        19.2     82.9                                      84      AR-6011  20        11.6     70.8                                      85      AR-6099  20        11.7     75.9                                      86      DER-668  20        15.6     76.3                                      ______________________________________                                    

EP-1001: EPIKOTE 1001, Yuka Shell Epoxy K.K.

EP-1004: EPIKOTE 1004, Yuka Shell Epoxy K.K.

EP-1009: EPIKOTE 1009, Yuka Shell Epoxy K.K.

AR-6071: ARALDITE 6071, CIBA-GEIGY (Japan) Limited

AR-6099: ARALDITE 6099, CIBA-GEIGY (Japan) Limited

DER-668: D.E.R. 668, Dow Chemical Japan Ltd.

EXAMPLES 87 TO 92

The procedure of Examples 75 to 80 each was repeated to produceholograms except that the cationic polymerization photoinitiatorp-nitrobenzyl-9,10-dianthacene-2-sulfonate used in Example 75 wasreplaced with DNB-105 (a sulfonic acid ester, available from MidoriKagaku Co., Ltd. ). The diffraction efficiency was also measuredsimilarly. The diffraction efficiency before the heating was alsomeasured similarly. Results of the evalution are shown in Table 19.

                  TABLE 19                                                        ______________________________________                                                     Amount of                                                        Aliphatic    exposure  Diffraction efficiency (%)                             Example monomer  (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        87      TEGDA    20        10.1     72.9                                      88      DEGDA    20        12.3     89.2                                      89      NPGDA    20        10.6     78.9                                      90      EKA      20         8.3     67.4                                      91      HDDA     20         9.3     71.0                                      92      TEGDMA   20         9.9     70.3                                      ______________________________________                                    

TEGDA: Triethylene glycol diacrylate

DEGDA: Diethylene glycol diacrylate

NPGDA: Neopentyl glycol diacrylate

EKA: Ethylcarbitol acrylate

HDDA: 1,6-Hexanediol diacrylate

TEGDMA: Triethylene glycol dimethacrylate

EXAMPLES 93 TO 97

The procedure of Example 76 was repeated to produce holograms exceptthat the spectral sensitizer 3,3'-carbonylbis(7-diethylaminocoumarin)used therein was replaced with Rose Bengale (RB),4,4'-dimethylaminochalcone (DMAC), 4,4'-bis(dimethylamino)benzalacetone(BDMABA), 3,3'-diethyl-2,2'-oxacarbocyanine iodide (DEOCCI) and2,4,6-triphenylthiapyrylium perchlorate (TPTPPC), respectively. Thediffraction efficiency was also measured similarly. The diffractionefficiency before the heating was also measured similarly. Results ofthe evalution are shown in Table 20.

                  TABLE 20                                                        ______________________________________                                                     Amount of                                                                     exposure  Diffraction efficiency (%)                             Example:                                                                              Sensitizer                                                                             (mJ/cm.sup.2)                                                                           Before heating                                                                         After heating                             ______________________________________                                        93      RB       30        8.2      65.1                                      94      DMAC     30        9.7      74.8                                      95      BDMABA   30        8.9      65.9                                      96      DEOCCI   30        8.1      67.3                                      97      TPTPPC   40        8.6      70.7                                      ______________________________________                                    

RB: Rose Bengale

DMAC: 4,4'-Dimethylaminochalcone

BDMABA: 4,4'-Bis(dimethylamino)benzalacetone

DEOCCI: 3,3'-Diethyl-2,2'-oxacarbocyanine iodide

TPTPPC: 2,4,6-Triphenylthiapyrylium perchlorate

The holograms according to Examples 75 to 97 caused no lowering ofdiffraction efficiency even after they were left in an environment of25° C., 60% RH for 180 days and in an environment of 150° C. for 10hours.

What is claimed is:
 1. A photosensitive recording material for use inproducing a volume type phase hologram, comprising:a solvent-soluble,cationic-polymerizable thermosetting bisphenol A type epoxy oligomer,the bisphenol A type epoxy oligomer being represented by Formula V:##STR12## wherein X represents a hydrogen atom or a halogen atom, and nis 1 to 20; and having an epoxy equivalent weight of 400 to 6,000 and amelting point of 60° C. or above; a radical-polymerizable aliphaticmonomer having at least one ethylenically unsaturated bond, thealiphatic monomer being liquid at normal temperature and pressure andhaving a boiling point of 100° C. or above at normal pressure; aphotoinitiator system selected from the group consisting of i) a firstphotoinitiator compound which simultaneously generates a radical speciesthat activates radical polymerization and a Br.o slashed.nsted acid orLewis acid that activates cationic polymerization, upon exposure to avisible light ray in the presence of a spectral sensitizer and uponsubsequent sensitization by the action of the latter, and ii) a secondphotoinitiator comprised of a mixture of a radical polymerizationphotoinitiator which generates a radical species that activates radicalpolymerization, upon exposure to the visible light ray in the presenceof a spectral sensitizer and upon subsequent sensitization by the actionof the latter, and a cationic polymerization photoinitiator whichgenerates a Br.o slashed.nsted acid or Lewis acid that activatescationic polymerization, upon exposure to the visible light ray in thepresence of a spectral sensitizer and upon subsequent sensitization bythe action of the latter; and said spectral sensitizer acting to absorbsaid visible light ray and to sensitize said first photoinitiatorcompound or said second photoinitiator, said aliphatic monomer beingmixed in an amount of from 20 parts by weight to 80 parts by weightbased on 100 parts by weight of said thermosetting bisphenol A typeepoxy oligomer.
 2. The photosensitive recording material for use inproducing a volume type phase hologram according to claim 1, whereinsaid aliphatic monomer is mixed in an amount of from 40 parts by weightto 70 parts by weight based on 100 parts by weight of said thermosettingbisphenol A type epoxy oligomer.
 3. The photosensitive recordingmaterial for use in producing a volume type phase hologram according toclaim 1 or 2, wherein said aliphatic monomer is a polyethylene glycoldiacrylate or -methacrylate, or propylene glycol diacrylate or-methacrylate represented by Formula VI: ##STR13## wherein R₅ to R₇ eachrepresent a hydrogen atom or a methyl group, m and n each are 0 or more,and m+n is 1 to
 20. 4. The photosensitive recording material for use inproducing a volume type phase hologram according to claim 1 or 2,wherein said first photoinitiator compound is selected from the groupconsisting of an iron arena complex, a trihalogenomethyl-substituteds-triazine, a sulfonium salt, a diazonium salt, an iodonium salt, aphosphonium salt, a selenonium salt and an arsonium salt.
 5. Thephotosensitive recording material for use in producing a volume typephase hologram according to claim 1 or 2, wherein said spectralsensitizer is a visible light ray-absorptive organic compound selectedfrom the group consisting of a cyanine compound, a merocyanine compound,a coumarin compound, a chalcone compound, e xanthene compound, athioxanthene compound, an azulenium compound, a squarilium compound, atetraphenylporphyrin compound, a tetrabenzoporphyrin compound and atetrapyrazino compound.
 6. A photosensitive recording medium for use inproducing a volume type phase hologram, comprising:a substrate; aphotosensitive layer formed by coating on the substrate a photosensitivesolution comprising photosensitive recording material, followed bydrying, said photosensitive recording material comprising: asolvent-soluble, cationic-polymerizable thermosetting bisphenol A typeepoxy oligomer, the bisphenol A type epoxy oligomer being represented byFormula V: ##STR14## wherein X represents a hydrogen atom or a halogenatom, and n is 1 to 20; and having an epoxy equivalent weight of 400 to6,000 and a melting point of 60° C. or above; a radical-polymerizablealiphatic monomer having at least one ethylenically unsaturated bond,the aliphatic monomer being liquid at normal temperature and pressureand having a boiling point of 100° C. or above at normal pressure; aphotoinitiator system selected from the group consisting of i) a firstphotoinitiator compound which simultaneously generates a radical speciesthat activates radical polymerization and a Br.o slashed.nsted acid orLewis acid that activates cationic polymerization, upon exposure to avisible light ray in the presence of a spectral sensitizer and uponsubsequent sensitization by the action of the latter, and ii) a secondphotoinitiator comprised of a mixture of a radical polymerizationphotoinitiator which generates a radical species that activates radicalpolymerization, upon exposure to the visible light ray in the presenceof a spectral sensitizer and upon subsequent sensitization by the actionof the latter, and a cationic polymerization photoinitiator whichgenerates a Br.o slashed.nsted acid or Lewis acid that activatescationic polymerization, upon exposure to the visible light ray in thepresence of a spectral sensitizer and upon subsequent sensitization bythe action of the latter; and said spectral sensitizer acting to absorbsaid visible light ray and to sensitize said first photoinitiatorcompound or said second photoinitiator; said aliphatic monomer beingmixed in an amount of from 20 parts by weight to 80 parts by weightbased on 100 parts by weight of said thermosetting bisphenol A typeepoxy oligomer; and an oxygen barrier layer provided on thephotosensitive layer.
 7. The photosensitive recording medium for use inproducing a volume type phase hologram according to claim 6, whereinsaid aliphatic monomer is mixed in an amount of from 40 parts by weightto 70 parts by weight based on 100 parts by weight of said thermosettingbisphenol A type epoxy oligomer.
 8. The photosensitive recording mediumfor use in producing a volume type phase hologram according to claim 6or 7, wherein said aliphatic monomer is a polyethylene glycol diacrylateor -methacrylate, or propylene glycol diacrylate or -methacrylaterepresented by Formula VI: ##STR15## wherein R₅ to R₇ each represent ahydrogen atom or a methyl group, m and n each are 0 or more, and m+n is1 to
 20. 9. The photosensitive recording medium for use in producing avolume type phase hologram according to claim 6 or 7, wherein said firstphotoinitiator compound is selected from the group consisting of an ironarene complex, a trihalogenomethyl-substituted s-triazine, a sulfoniumsalt, a diazonium salt, an iodonium salt, a phosphonium salt, aselenonium salt and an arsonium salt.
 10. The photosensitive recordingmedium for use in producing a volume type phase hologram according toclaim 6 or 7, wherein said spectral sensitizer is a visible lightray-absorptive organic compound selected from the group consisting of acyanine compound, a merocyanine compound, a coumarin compound, achalcone compound, a xanthene compound, a thioxanthene compound, anazulenium compound, a squarilium compound, a tetraphenylporphyrincompound, a tetrabenzoporphyrin compound and a tetrapyrazino compound.11. A process for producing a volume type phase hologram, comprising thesteps of:subjecting a photosensitive layer of a photosensitive recordingmedium to holographic exposure to a visible light ray as a light sourceto form a latent image, substantially directly followed by heating at atemperature of from 60° C. to 120° C. for 1 minute to 30 minutes toproduce a volume type phase hologram, said photosensitive recordingmedium comprising:a substrate; a photosensitive layer formed by coatingon the substrate a photosensitive solution comprising a photosensitiverecording material, followed by drying, said photosensitive recordingmaterial comprising: a solvent-soluble, cationic-polymerizablethermosetting bisphenol A type epoxy oligomer, the bisphenol A typeepoxy oligomer being represented by Formula V: ##STR16## wherein Xrepresents a hydrogen atom or a halogen atom, and n is 1 to 20; andhaving an epoxy equivalent weight of 400 to 6,000 and a melting point of60° C. or above; a radical-polymerizable aliphatic monomer having atleast one ethylenically unsaturated bond, the aliphatic monomer beingliquid at normal temperature and pressure and having a boiling point of100° C. or above at normal pressure; a photoinitiator system selectedfrom the group consisting of i) a first photoinitiator compound whichsimultaneously generates a radical species that activates radicalpolymerization and a Br.o slashed.nsted acid or Lewis acid thatactivates cationic polymerization, upon exposure to a visible light rayin the presence of a spectral sensitizer and upon subsequentsensitization by the action of the latter, and ii) a secondphotoinitiator comprised of a mixture of a radical polymerizationphotoinitiator which generates a radical species that activates radicalpolymerization, upon exposure to the visible light ray in the presenceof a spectral sensitizer and upon subsequent sensitization by the actionof the latter, and a cationic polymerization photoinitiator whichgenerates a Br.o slashed.nsted acid or Lewis acid that activatescationic polymerization, upon exposure to the visible light ray in thepresence of a spectral sensitizer and upon subsequent sensitization bythe action of the latter; and said spectral sensitizer acting to absorbsaid visible light ray and to sensitize said first photoinitiatorcompound or said second photoinitiator; said aliphatic monomer beingmixed in an amount of from 20 parts by weight to 80 parts by weightbased on 100 parts by weight of said thermosetting bisphenol A typeepoxy oligomer; and an oxygen barrier layer provided on thephotosensitive layer.
 12. The process for producing a volume type phasehologram according to claim 11, wherein said aliphatic monomer is mixedin an amount of from 40 parts by weight to 70 parts by weight based on100 parts by weight of said thermosetting bisphenol A type epoxyoligomer.
 13. The process for producing a volume type phase hologramaccording to claim 11 or 12, wherein said aliphatic monomer is apolyethylene glycol diacrylate or -methacrylate, or propylene glycoldiacrylate or -methacrylate represented by Formula VI: ##STR17## whereinR₅ to R₇ each represent a hydrogen atom or a methyl group, m and n eachare 0 or more, and m+n is 1 to
 20. 14. The process for producing avolume type phase hologram according to claim 11 or 12, wherein saidfirst photoinitiator compound is selected from the group consisting ofan iron arene complex, a trihalogenomethyl-substituted s-triazine, asulfonium salt, a diazonium salt, an iodonium salt, a phosphonium salt,a selenonium salt and an arsonium salt.
 15. The process for producing avolume type phase hologram according to claim 11 or 12, wherein saidspectral sensitizer is a visible light ray-absorptive organic compoundselected from the group consisting of a cyanine compound, a merocyaninecompound, a coumarin compound, a chalcone compound, a xanthene compound,a thioxenthene compound, an azulenium compound, a squarilium compound, atetraphenylporphyrin compound, a tetrabenzoporphyrin compound and atetrapyrazino compound.